The research for the coming year will involve generalizing some of our results from the single loop multiplier model to multiple tube models. Existence and uniqueness of solutions of systems of differential equations for these n tube models will be investigated. Also, upper and lower bounds for these concentrations will be determined. A multi-tube model will be studied numerically using our numerical inversion technique for Laplace transforms. An effort will be made to generalize this inversion technique to nonlinear models. BIBLIOGRAPHIC REFERENCES: Crump, K. S. "Numerical Inversion of Laplace Transforms Using a Fourier Series Approximation, "Journal of the Association for Computing Machinery, vol. 23, no. 1, January 1976, pp. 89-96. Johnson, A. M. and Crump, K. S. "Transient Solution of a Solute Cycling Model of the Renal Medulla by Using Laplace Transforms," Proceedings of the 1976 Summer Simulation Conference (in press).